Eric Bryan studies the design of a deadly 16th Century Korean war-vessel.

In 1591, with the threat of foreign invasion in mind, Korean Admiral Yi Sunshin collaborated on the design of a vessel called a kobukson, or ‘turtle ship’. The ship was based partly on a design going back to at least the early 16th Century, and partly on the standard Korean warship, the panokseon. Admiral Yi and his team completed the first new turtle ship in 1592, in time for its participation in the Seven Year War (1592-1598).

Dimensions and construction

Allowing for variations between individual vessels, the turtle ship was an ark-like vessel of 100 to 120 feet in length, 20 or more feet in height, with a beam of 30 or more feet. It had two sails each with a fold-down mast, a dragon’s head at the bow, and a tail at the stern.

Most distinctively, the vessel had a turtle shell-like roof capping the top deck. This shell was covered in heavy planking and bristling with protruding iron spikes to deter enemy boarders. A turtle ship’s crew could camouflage the spikes with mats, empty sacks, thatch, or straw, creating a minefield of sharp points and blades to greet unsuspecting raiders.

There is controversy over whether or not the shell of the turtle ship was iron-armoured. Contemporary Korean sources refer to the spikes, but a contemporary Japanese record mentions turtle boats being ‘covered in iron’. Whether the latter reference indicates iron plating or simply a thick peppering of iron spikes is still debated.

Some vessels had a gargoyle-like face painted below the dragon’s head, which was a reinforced structure for ramming.

The frame of the ship was constructed of interlocking beams, perhaps using a mortise and tenon method or something similar. The vessels are believed to have been made of spruce, red pine, or other dense wood so that the ship could carry heavy armament and withstand cannon recoil. Nails or fasteners of the same wood may have been used in place of iron, not only to avoid rusting, but because their expansion when exposed to water would further tauten the joints.

The turtle ship had two interior decks: the lower for the oarsmen; the upper for the gunners and archers. (In one Japanese painting, the ships were portrayed as three-deck leviathans with soldiers, archers, and gunners each on separate decks.) The ship’s fortress-like design allowed its occupants to view outside, while they remained invisible to their enemies.

Armament, propulsion, and crew

Besides the sails, a turtle ship had eight to 10 oars per side – each operated by as many as four oarsmen and one leader – which powered the vessel. This aspect made the ship highly manoeuvrable and adept as a close-combat vessel.

A turtle ship’s crew might be made up of 80 non-combatants and 45 combatants, depending on its quantity of oars and cannon. While its non-combatants were rowers and rowing leaders, its combatants were gunners, munitions chargers, and archers.

With typically six to 11 cannon ports per side, a turtle ship also had two cannon ports each in the bow and stern, allowing the vessel to fire in any direction. A turtle ship carried a range of light to heavy cannon. The medium-range cannon could shoot flaming arrows or cannonballs. The heaviest cannon, called Chon (Heaven), had a range of perhaps over 650 yards.

The dragon’s head at the bow of the ship was not purely an intimidating ornament of psychological warfare. The edifice was so designed so that a cannon could be fired through its mouth, propelling cannonballs or flaming arrows from its jaws. Some turtle ships’ dragon’s heads could expel clouds of noxious vapour created from a saltpetre and sulphur mixture. This tactic could not only leave enemies choking and gasping, but provide a smokescreen to mask the turtle ship’s manoeuvres.
The turtle ship design was used into the nineteenth century.